Reciprocating pumps and in particular fuel injection pumps for internal combustion engines



Sept. 10; 1963 P. E. BESSIERE 3,103,174 RECIPROCATING P S AND IN PARTICULAR FUEL INJECTION PUMPS FOR INTERNAL COMBUSTION ENGINES Filed Dec. 11. I958 3 Sheets-Sheet 1 INVEN TOR P 1963 P. E. BE'SSIERE 3,103,174

RECIPROCATING PUMPS AND IN PARTICULAR FUEL INJECTION PUMPS FOR INTERNAL COMBUSTION ENGINES Filed Dec. 11, 1958 3 Sheets-Sheet 2 /NVENTOR t BeJm'cr- ATTURN Y5 p 1963 P. E. BESSIERE 3,103,174

RECIPRQCATING PUMPS AND IN PARTICULAR FUEL INJECTION PUMPS FOR INTERNAL COMBUSTION ENGINES Filed Dec. 11, 1958 V 3 Sheets-Sheet 3 INVEN TOR Pier-m: Ef'ienna Bea-sir.

ATTOR 'YS 3,103,174 RECIPROCATING PUMPS AND IN PARTICULAR FUEL INJECTION PUMPS FOR INTERNAL COM- BUSTION ENGINES Pierre Etienne Bessire, 55 Blvd. Command Charcot,

N enilly-sur-Seine, France Filed Dec. 11, 1958, Ser. No. 779,640 Claims priority, application France Dec. 24, 1957 11 Claims. (Cl. 103-41) The present invention relates to self-regulating reciprocating pumps and in particular to fuel injection pumps tor internal combustion engines.

The pumps with which my invention is concerned include a discharge conduit the opening of which prevents the pump from delivering liquid, this discharge conduit being controlled by valve means urged by resilient rneans toward discharge conduit closing position and actuated to open this discharge conduit by a control fluid, this control fluid being made to flow, through a circulation circuit having a normally open outlet for the outflow of said fluid, during every outward stroke of the pump piston and at a flow rate directly proportional to the speed of "said piston, an increase of said flow rate above a given value causing said outlet to be closed, thus causing in said circuit a sudden rise of the fluid pressure which brings said valve means into discharge conduit opening position. The object of my invention is to provide a pump of this type which is better adapted to meet the requirements of practice than those used up to the present time.

For this purpose, according to my invention, the beginning of every flow of control fluid through said circulation circuit has a given constant phase advance with respect to the beginning of the liquid delivery portion of every outward stroke of said pump piston, whereby, for a given frequency of reciprocation of said piston, said valve means are brought into discharge conduit opening condition before the beginning of the delivery portion of every outward stroke of the pump piston and no liquid delivery takes place.

Preferred embodiments of the present invention will be hereinafter described with reference to the accompanying drawings, given merely by way of example and in which:

FIGS. 1 and 2 diagrammatically show, in axial section, a fuel injection pump made according to a first embodiment of the present invention, the parts being shown in two relative different positions in said figures respectively.

FIG. 3 is a view, similar to FIG. 1, showing another embodiment of the invention.

The pump shown by the drawings includes a piston 1 driven in such manner, for instance by means of a cam (shown only by FIG. 3), that the movement of the piston is accelerated from the time, at the beginning of its upward stroke, when 'fuel starts being compressed and delivered. The downward stroke thereof is obtained by means of a return spring 2, as shown by FIGS. 1 and 2.

Piston 1 reciprocates in a cylinder 3 into which opens, at 4a, a feed conduit 4 through which fuel arrives in the usual manner from an auxiliary pump (not shown). Furthermore, a delivery conduit 5 provided with a checkvalve 6 leads out from said cylinder 3. This delivery conduit 5 conveys the fuel delivered by the pump toward the injector or injectors (not shown) of the engine fed by the pump.

A discharge conduit 7 also leads from the top of cylinder 3, either directly (FIGS. 1 and 2) or through a portion of conduit 5 (FIG. 3), to the outside. This discharge conduit 7 is controlled by a moving element 8 con sisting for instance of a slide valve.

Piston 1, during its upward stroke and after it has closed port 4a, delivers tuel into conduit 5 as long as United States Patent 0 3,103,174 Patented Sept. 10, 1963 slide valve 8 keeps discharge conduit 7 closed. But fuel delivery through conduit 5 ceases as soon as slide valve 8 opens discharge conduit 7.

i The description will now deal first with the embodiment of FIGS. 1 and 2.

In order to control slide valve 8, I apply thereto, on the one hand a downwardly directed force preferably produced by a return spring 9, for instance adjustable by means of a screw 10, and on the other hand the upwardly directed thrust of a fluid (and in particular a liquid) receiving pressure impulses at a frenquency equal to that of the reciprocating movement of piston 1, this pressure reaching, during the upward strokes of piston 1, peak values which increase, as the speed at which the pump is driven (i.e. the speed of the engine ted by the pump) increases, up to a value for which said presure overcomes the resistance of spring 9. Then, for speeds exceeding this value, the liquid pressure capable of overcoming the resistance of spring 9 is reached for shorter and shorter upward displacements of piston 1.

In order to produce said pulsating pressure of the liquid used to actuate slide valve 8, I make use of an auxiliary reciprocating pump including an auxiliary piston 11 fitting slidably in an auxiliary cylinder 12. Cylinder 12 is provided with a feed conduit 13, also preferably connected with the delivery of a primary pump (not shown) which may be the same as that which supplies liquid to conduit 4. A delivery conduit 14, leading from auxiliary cylinder 12 and containing a check-valve 15, is in communication with one of the ends of a cylinder 16 in which slide valve 8 is slidably fitted, the pressure of the liquid in conduit 14- acting against the thrust of return spring 9 on slide valve 8.

According to a particularly simple construction illustrated by the drawing, the main piston 1 and the auxiliary piston 11 form a single unit and cylinders 3 and 12 are in line and coaxial with each other. In this case, return spring 2 may be housed in cylinder 12, this spring being common to both of the pistons 11 and 1, which are driven by the same cam.

In order to comply with the above stated conditions concerning the pressure of the liquid delivered by piston 11, this liquid is caused to pass through a throttled passage controlled by slide valve 8 itself. A conduit '17 branching out from conduit 14, for instance from the portion 14a thereof located downstream of cylinder 16, opens into the wall of cylinder 16 opposite a discharge conduit 17a in line with conduit 17. Slide valve 8 is provided with a groove 19 located at a level such that, when slide valve 8 is in its position of rest (where the bottom end of said slide valve is "applied against an abutment 20 as shown by FIG. 1), the lower edge of groove 19 and the opening of conduit '17 into cylinder 16 limit between them a throttled passage 21 through which the liquid delivered by piston 11 must flow to pass into discharge conduit 17a.

The initial value of the cross-section of this throttled passage depends upon the position of abutment 20, which position is preferably adjustable by means of a screw 22.

It will be seen that as soon as the pressure of the liquid delivered by piston 11 reaches a value suflicient to overcome the thrust of return spring 9, the area of the cross-section of throttled passage 21 decreases, and quickly becomes equal to zero. If, at this time, piston 11 has not yet reached the end of its upward stroke, slide valve 8 is suddenly pushed upwardly until a second groove 23, provided in slide valve 8 below groove 19, comes opposite conduits '17 and 17a and thus enables the liquid still delivered by piston 11 to flow to the outside. This movement of slide valve 8 simultaneously brings opposite discharge conduit 7 a third groove 24 provided in slide valve w 8 above groove 19, whereby conduit 7 places cylinder 3 in communication with the outside.

In order to give the variations of the cross-section area of throttled passage 21 a law diflerent from the linear law obtained with groove 19, I may replace this groove 24 by a passage extending throughout the slide valve and having a suitable cross-section, for instance a circular, triangular or other cross-section, which, in cooperation with the cross-section (also of suitable shape) of the opening of conduit -17 into cylinder 16, permits of obtain ing the desired law of variation.

In order to obtain the return of slide valve 8 to its position of rest immediately after the beginning of every downward stroke of pistons 11 and 1, the portions 14a of delivery conduit 14 is placed in communication, during every downward stroke of piston 11, with a discharge conduit 14b bypassing throttled passage 21, this conduit 1412 being of course closed during every upward (delivery) stroke of piston 11.

In order to control this discharge conduit 14b, I advantageously make use of a slide valve actuated in synchronisrn with the reciprocating movement of piston 11 by means of the pressure of the liquid present in cylinder -12. For this purpose, one of the ends of cylinder '26, in which slide valve 25 is movable, is connected through a conduit 27 to cylinder 12, or delivery conduit 14. In this last case, which is that illustrated by the drawings, the point of conduit 14 from which value which, as long as slide valve 8 is not lifted, i.e.

conduit 27 branches out is located upstream of checkposition of rest during every downward stroke of piston -11 and it is moved away from this position, thus closing the communication with dischange conduit 141) during every upward stroke of piston'11.

In the embodiment of my invention shown by the drawings, conduits 4 and 13 open into the respective cylinders 3 and 12 at points such that, during every upward stroke of pistons '1 and 11, piston 11 completely closes conduit 13 and starts compressing liquid and delivering it from cylinder 12 before piston 1 starts to close conduit 4 and delivers liquid from cylinder 3 toward delivery conduit 5. The distance between the leading edge (that is, the lower edge in FIG. 1) of the opening of the liquid feed conduit 4 into said chamber 3 at such intermediate point and the position occupied by the said main piston edge (the upper face in FIG. 1) when said main piston is at the end of its return stroke is substantially greater than the distance between the trailing edge (the upper edge in FIG. 1) of the opening of said fluid feed conduit into said auxiliary cylinder at such intermediate point thereof and the position occupied by said auxiliary piston edge (the upper face in FIG. 1) at the end of its return stroke. Thereby, during the out- -ward strokes of said main and auxiliary pistons the fluid feed conduit is completely closed by said auxiliary piston a substantial time before the commencement of the closing'of said liquid feed conduit by said main piston, thereby preventing delivery of fuel through said delivery conduit at high speed of operation.

FIG. 1 shows the parts in the position they occupy when pistons 1 and 11 are approximately in their lower dead center position.

This pump works as follows.

7 Since pistons 11 and 1 are supposed to undergo an acceleration during every upward stroke thereof, even when the engine on which the pump is mounted runs at a constant speed, the pressure of the liquid which, during every upward stroke of piston 11, flows through the throttled passage 21, rises during said stroke up to a for relatively low values of the speed of the engine on which the pump is mounted, increases when said speed increases. For a given value of the engine speed, this liquid pressure, which acts upon the lower end face of slide valve 8 becomes sufliciently high to overcome the resistance of spring 9 and slide valve 8 starts moving upwardly. This movement further reduces the crosssection area of throttled passage 21 which, in turn, increases the liquid pressure acting on the lower end face of valve 8 and further accelerates the reduction of the cross-section area of throttled passage 21. Full closing of throttled passage 21 and upward displacement of slide valve 8 to the position where it opens discharge conduit 7 are therefore practically instantaneous. Slide valve 8 then remains in its upper position (FIG. 2) until the end of the upward stroke of piston 11, groove 23 opening the communication between conduit 17, 17a by an amount just sufficient to keep it in this position.

For higher and higher speeds of the engine above the above mentioned value, this opening of discharge conduit 7 takes place for shorter and shorter upward strokes of piston 11. As long as the opening of discharge conduit 7 takes place after inlet conduit 4 has been closed by piston 1, some amount of fuel is delivered by piston 1 through delivery conduit 5 toward the injector or injectors to be fed by the pump but this amount decreases as the speed of the engine (i.e. the frequency of reciprocation of pistons 1 and 11) increases. It becomes zero if, due to the delay between the closing of conduit 13 by piston 11 and the closing of conduit 4 by piston 1, the opening of discharge conduit 7 takes place before the closing of conduit 4. In this case, no injection takes place and the speed (number of reciprocations of the pump per unit of time) for which injection thus ceases is a top speed which can never be exceeded by the engine on which the pump is fitted for injection of fuel thereto.

In order to vary this top-speed, it suflices to vary the force exerted by spring 9 by adjustment of screw 10. The top speed may also be varied by modifying the posi tion of rest of slide valve 8 by means of screw 22 which controls the position of abutment 20.

Thus, in the pump above described, the control fluid supplied by the auxiliary pump 1112 is caused to flow through a circulation circuit 14--14a1717t7 having a normally open outlet 17a. And this outlet is closed when the flow rate of fluid flowing through the above mentioned circuit under the action of piston 11 reaches a given value. The effect of this flow rate is to cause the pressure at the lower end of cylinder 16 to become high enough to move slide valve 8 sufliciently in the ward direction to close the outlet 17a.

In the pump illustrated by FIG. 3,-the same result is obtained in a different manner.

The general construction of this pump is very similar to that of the pump of FIGS. 1-2. The same parts are designated by the same reference numerals.

The essential difference between this construction and that of FIGS. 1-2 is that the closing of the outlet of the circuit through which flows the fluid delivered by auxiliary pump 11-12 (which circuit comprises in this case the elements 14-1644-46-47) instead of being produced by the pressure of this fluid acting on the lower end face of slide valve 8 is produced by the driving action ofthis fluid'flowing through a cylindrical chamber 16 on a ball 39 movable in this chamber and of a diameter a little smaller than the inner diameter of said chamber 16. On every stroke of piston 11, ball 39 is driven upwardly in chamber 16, up to a level which depends upon the flow rate of the liquid passing through this chamber; For a given value of this flow rate, ball 39 reaches the valve seat 48 formed at the lower end of passage '44 and the outlet 47 of the above mentioned circuit is cut-01f. As in the case of FIGS. 1-2, slide valve 8 is then compelled by this fluid to move upwardly and its groove 24 opens the discharge conduit 7 of the main pump 1-2. At the same time, outlet passage 50 is partly cleared by slide valve '8 so that liquid can escape from said chamber 16.

In this pump construction, the top and bottom positions of slide valve 8 are determined by a shoulder 51 and a shoulder 52 forming abutments for the enlarged top end of slide valve 8.

A check-valve constituted by a ball 54 urged toward its seat by a spring 55 constantly maintains a minimum pressure in discharge conduit 7. This ball valve 54 is interposed between discharge conduit 7 proper and its outlet portion 53.

The position of rest of ball 39 is determined by an abutment constituted by the end of a screw 57 so that this position is adjustable.

The operation of the pump of FIG. 3 is as follows:

If the speed of the engine fed by the pump is low, the upward flow of liquid through chamber 16 does not move ball 39 sufiiciently high, on every piston stroke, to apply it on seat 48. Discharge conduit 7 is therefore never opened in these conditions. The amount of fuel delivered by the pump on every piston stroke is maximum.

If the engine speed (and therefore the flow rate, or velocity, of the fluid flowing through chamber 16) increases, ball 39 is applied on seat 48, which causes slide valve 3 to open discharge conduit 7, before the end of the delivery stroke of piston 1 (this end occurring when the horizontal branch of conduit 37 provided in piston 1 comes opposite feed conduit 4). The amount of liquid elivered by pump 1-3 during a piston stroke is there fore reduced.

This reduction becomes more and more important as the frequency of reciprocation of pistons l11 increases. This is due to the fact that the velocity of the upward movement of ball 39 increases more rapidly than the velocity of the liquid by which it is driven. As a matter of fact, the drag of the ball with respect to the liquid 7 is proportional to v, 11 being the velocity of this liquid and n being greater than 1.

If the speed of the engine further increases, the velocity of ball 39 increases to a value such that it is applied upon its seat 48, and discharge conduit 7 is opened, before piston 1 has moved a distance it necessary to close feed conduit 4 and has become capable of delivering liquid from cylinder 3. Any injection is then impossible and the spied at which this takes place is a top' limit speed for the engine.

The regulating action may be varied by varying either the position of rest of ball 39 (by means of screw 57) or the value of the force urging said ball downwardly ,(which force might be supplied, in addition to the effect of gravity, by "a return spring, possibly adjustable).

Of course, adjustment of any element making it possible to modify the regulation conditions of the pump may be placed under control of a governor, in particular a speed governor such as a centrifugal governor. An example of such an arrangement is disclosed in my French patent application Ser. No. 742,761, filed on July 8, 1957 for Improvements Brought to Hydraulic Speed Governors, in Particular for Fuel Injection Pumps.

in a general manner, while I have, in the above description, disclosed what I deem to be practical and eificient embodiments of my invention, it should be well understood that I do not wish to be limited thereto as there might be changes made in the arrangement, disposition and form of the parts Without departing from the principle of the present invention as comprehended within the scope of the accompanying claims.

What I claim is:

1. A pump which comprises, in combination, a cylinder, a piston fitting slidably in said cylinder and having a reciprocating movement therein, a liquid delivery circuit leading from one end of said cylinder, so that liquid can be delivered from said cylinder through said circuit during the compression strokes of said piston, feed conduit means opening into said cylinder for filling said cylinder with liquid during the suction strokes of said piston, a discharge conduit leading from said end of said cylinder and opening to the outside thereof, a cylindrical casing transverse to said discharge conduit and intersecting it so that a length of said discharge conduit consists of a portion of said casing, a slide valve fitting slidably in said cylindrical casing and movable therein to control the discharge of quid from said cylinder to the outside thereof through said conduit, whereby opening of said discharge conduit by said valve means during a compression stroke of said piston prevents the delivery of liquid through said delivery circuit, resilient means for constantly urging said slide valve toward discharge conduit closing position, one end of said cylindrical casing forming a chamber such that expansion thereof causes said slide valve to move toward discharge conduit opening position, means operatively connected with said piston for feeding into said chamber, during every compression stroke of said piston, a fluid stream at a how rate constantly increasing for a time, the rate of increase of said flow rate being the higher as the number of reciprocations of said piston per unit of time is higher, said means for feeding a fluid stream to said chamber during every compression stroke of said piston being arranged to start feeding each fluid stream with a constant phase advance with respect to the beginning of the corresponding compression stroke of said piston, an outlet conduit leading from said chamberand having a length there of constituted by a portion of said casing, said slide valve being provided with a groove arranged to cooperate with said outlet conduit and to clear it partly, when said slide valve is in the position where the volume of said chamber is minimum, to such a degree that expansion of the volume of said chamber causes a reduction of the cross-section area of said outlet conduit thus cleared by said groove, said slide valve being provided with another groove, arranged to clear said outlet conduit when said slide valve is in discharge conduit opening position, whereby said fluid can then be. discharged to the outside through said outlet conduit, said casing being so dimensioned that, for a given value of said frequency of reciprocation of said piston, the fluid fed into said chamber reaches a pressure capable of overcoming the action of said resilient means and of bringing said slide valve into discharge conduit opening position.

2. A pump according to claim 1 further including a fluid discharge conduit leading to the outside from.- the portion of said outlet conduit located upstream of said slide valve and valve means in said last mentioned discharge conduit operatively connected with said piston for closing said last mentioned discharge conduit during the outward strokes of said piston and opening said last mentioned discharge conduit during the return strokes of said piston.

3. A pump according to claim 1 further including means for adjusting said resilient means.

4. A pump according to claim 1 further including means for adjusting the limit position toward which said slide valve is urged by said resilient means.

5. A pump according to claim 1 in which said means for feeding fluid into said chamber include a cylinder coaxial with said first mentioned cylinder and in fixed position with respect thereto, a piston rigid with said first mentioned piston and fitting slidably .in said second mentioned cylinder and feed conduit means opening into said second mentioned cylinder and positioned so that the delivery stroke of said second piston begins before the delivery stroke of said pump piston, said pump further including a conduit leading from said second mentioned cylinder to said chamber, and a check-valve in said last mentioned conduit mounted to open only toward said chamber.

6. A liquid pump which comprises, in combination, a main cylinder, a main piston fitting slidably in said cylinder and having a reciprocating movement therein, so as to limit therewith a variable volume working space, the movements of said piston in said cylinder in the direction for which the volume of said working space is reduced being called outward strokes and those in the the opposed direction return strokes, a liquid feed conduit opening into the side wall of said cylinder at an 'intermediate point thereof, a liquid delivery conduit leading from said working space, a discharge conduit leading from said Working space to the outside thereof so that, on every outwardstroke of said main piston, liquid is forced by said main piston toward said delivery circuit and said discharge conduit during the period elapsing from the time the edge of said main piston passes at said intermediate point of said cylinder side wall to the time said main piston reaches the end of said outward stroke, a valve movable in a portion of said discharge conduitto control the outflow of liquid from said main cylinder through said discharge conduit, whereby, during every above mentioned period of the movement of said main piston, liquid is not fed to said delivery circuit when said valve is in discharge conduit opening position, resilient means for constantly urging said valve toward discharge conduit closing position, an auxiliary pump including two parts movable with respect to each other, said parts being an auxiliary cylinder and an auxiliary piston fitting slidably in said auxiliary cylinder so as to limit between said two parts a variable volume chamber, the movements of said auxiliary piston in said auxiliary cylinder for which the volume of said chamber is reduced being called outward strokes and those in the opposed direction return strokes, means for operatively connecting one of said parts with said main cylinder and the other of said parts with said main piston so that said auxiliary pump is operated in synchronism with the reciprocating movement of said main piston in said main cylinder and the outward strokes of said auxiliary piston take place at the same time as the outward strokes of said main piston, a control circuit leading from said variable volume chamber, a fluid feed conduit opening into the side wall of said auxiliary cylinder at an intermediate point thereof, so that on every outward stroke of said auxiliary piston, fluid is forced by said auxiliary piston through said control circuit during the period elapsing from the time the edge of said auxiliary piston passes at said intermediate point of said auxiliary cylinder side wall to the time said auxiliary piston reaches the end of its outward stroke, said control circuit having a normally open outlet passage for the fluid flowing therethrough and means in said control circuit responsive to variations of the fluid flow rate in said control circuit for closing said outlet passage for a given value of said flow rate, said valve being operative by the fluid pressure in said control fluid circuit to be moved into discharge conduit opening position in response to the closing of said outlet, the distance between the leading edge of the opening of the liquid feed conduit into said chamber at such intermediate point and the position occupied by the said 7. A pump according to claim 6 including means for reciprocating said auxiliary piston arranged so that the movement thereof is accelerated during at least a portion of every outward stroke of said auxiliary piston beyond the position in which its edge passes at said intermediate point of said auxiliary cylinder to force fluid throughsaid control circuit so that the rate of increase of the fluid pressure in said control circuit during said stroke portions is the higher as the frequency of reciprocation of said auxiliary piston is higher.

8. A pump according to claim 6 in which said valve is a slide valve having a transverse surface subjected to the action of thefluid pressure in said control circuit so as to be urged toward discharge conduit opening position by said fluid pressure and said outlet passage comprises a throttled section controlled by said slide valve so as to tend to be gradually closed as said valve is being ing an orifice in one end face of said slide valve and forming a portion of said control circuit outlet passage, said control circuit comprising an elongated chamber one end of which is formed by said slide valve end face and the other end of which is connected with said auxilary cylinder end, a regulating member or" a cross section a little smaller than that of said chamber movable therein under the effect of the stream of fluid flowing therethrough, said regulating member being adapted to close said channel orifice when moved by said fluid stream into contact with said slide valve end face, said slide valve being mounted to be moved into discharge conduit opening position by the fluid pressure in said chamber when said channel orifice is thus closed by said member. j

10. A pump according to clairn 9 in which' aaid regulating member is a ball, said channel orifice i eing in the form of a ball seat adapted to cooperate with said ball acting as a valve to close said orifice.

11. In a device as claimed in claim 6, a check valve in said outlet passage for preventing flow of fluid therethrough in a direction towards said variable volume chamber.

References Qited in the file-of this patent UNITED STATES PATENTS 2,958,290 Bessiere Nov. 1, 1960 3,027,843 Raibaud Apr. 3, 1962 FOREIGN PATENTS 765,942 France lune 18, 1934 1,139,068 France Feb. 4, 1957 1,150,997 France Aug. 19, 1957 1,154,485 France Nov. 4, 1957 523,163 Great Britain July 8, 1940 58,441 Netherlands Sept. 17, 1946 

1. A PUMP WHICH COMPRISES, IN COMBINATION, A CYLINDER, A PISTON FITTING SLIDABLY IN SAID CYLINDER AND HAVING A RECIPROCATING MOVEMENT THEREIN, A LIQUID DELIVERY CIRCUIT LEADING FROM ONE END OF SAID CYLINDER, SO THAT LIQUID CAN BE DELIVERED FROM SAID CYLINDER THROUGH SAID CIRCUIT DURING THE COMPRESSION STROKES OF SAID PISTON, FEED CONDUIT MEANS OPENING INTO SAID CYLINDER FOR FILLING SAID CYLINDER WITH LIQUID DURING THE SUCTION STROKES OF SAID PISTON, A DISCHARGE CONDUIT LEADING FROM SAID END OF SAID CYLINDER AND OPENING TO THE OUTSIDE THEREOF, A CYLINDRICAL CASING TRANSVERSE TO SAID DISCHARGE CONDUIT AND INTERSECTING IT SO THAT A LENGTH OF SAID DISCHARGE CONDUIT CONSISTS OF A PORTION OF SAID CASING, A SLIDE VALVE FITTING SLIDABLY IN SAID CYLINDRICAL CASING AND MOVABLE THEREIN TO CONTROL THE DISCHARGE OF LIQUID FROM SAID CYLINDER TO THE OUTSIDE THEREOF THROUGH SAID CONDUIT, WHEREBY OPENING OF SAID DISCHARGE CONDUIT BY SAID VALVE MEANS DURING A COMPRESSION STROKE OF SAID PISTON PREVENTS THE DELIVERY OF LIQUID THROUGH SAID DELIVERY CIRCUIT, RESILIENT MEANS FOR CONSTANTLY URGING SAID SLIDE VALVE TOWARD DISCHARGE CONDUIT CLOSING POSITION, ONE END OF SAID CYLINDRICAL CASING FORMING A CHAMBER SUCH THAT EXPANSION THEREOF CAUSES SAID SLIDE VALVE TO MOVE TOWARD DISCHARGE CONDUIT OPENING POSITION, MEANS OPERATIVELY CONNECTED WITH SAID PISTON FOR FEEDING INTO SAID CHAMBER, DURING EVERY COMPRESSION STROKE OF SAID PISTON, A FLUID STREAM AT A FLOW RATE CONSTANTLY INCREASING FOR A TIME, THE RATE OF INCREASE OF SAID FLOW RATE BEING THE HIGHER AS THE NUMBER OF RECIPROCATIONS OF SAID PISTON PER UNIT OF TIME IS HIGHER, SAID MEANS FOR FEEDING A FLUID STREAM TO SAID CHAMBER DURING EVERY COMPRESSION STROKE OF SAID PISTON BEING ARRANGED TO START FEEDING EACH FLUID STREAM WITH A CONSTANT PHASE ADVANCE WITH RESPECT TO THE BEGINNING OF THE CORRESPONDING COMPRESSION STROKE OF SAID PISTON, AN OUTLET CONDUIT LEADING FROM SAID CHAMBER AND HAVING A LENGTH THEREOF CONSTITUTED BY A PORTION OF SAID CASING, SAID SLIDE VALVE BEING PROVIDED WITH A GROOVE ARRANGED TO COOPERATE WITH SAID OUTLET CONDUIT AND TO CLEAR IT PARTLY, WHEN SAID SLIDE VALVE IS IN THE POSITION WHERE THE VOLUME OF SAID CHAMBER IS MINIMUM, TO SUCH A DEGREE THAT EXPANSION OF THE VOLUME OF SAID CHAMBER CAUSES A REDUCTION OF THE CROSS-SECTION AREA OF SAID OUTLET CONDUIT THUS CLEARED BY SAID GROOVE, SAID SLIDE VALVE BEING PROVIDED WITH ANOTHER GROOVE, ARRANGED TO CLEAR SAID OUTLET CONDUIT WHEN SAID SLIDE VALVE IS IN DISCHARGE CONDUIT OPENING POSITION, WHEREBY SAID FLUID CAN THEN BE DISCHARGED TO THE OUTSIDE THROUGH SAID OUTLET CONDUIT, SAID CASING BEING SO DIMENSIONED THAT, FOR A GIVEN VALUE OF SAID FREQUENCY OF RECIPROCATION OF SAID PISTON, THE FLUID FED INTO SAID CHAMBER REACHES A PRESSURE CAPABLE OF OVERCOMING THE ACTION OF SAID RESILIENT MEANS AND OF BRINGING SAID SLIDE VALVE INTO DISCHARGE CONDUIT OPENING POSITION. 